1. Field of the Invention
The present invention relates to a machine tool having a function of inspecting a deteriorated state of a spindle of the machine tool.
2. Description of the Related Art
A spindle of a machine tool has a durable life. When the spindle is used for a long period of time, the spindle is deteriorated, and deterioration in machining accuracy and a rotation failure due to seizure or the like of a bearing sometimes occur. When such failures occur, repair is necessary. However, the seizure or the like of the bearing sometimes occurs without a sign. In such a case, the spindle needs to be urgently repaired in order to maintain production of a factory. However, when a replacement component cannot be immediately acquired, the production ability of the factor substantially decreases. Therefore, if a deteriorated state of the spindle is inspected and a sign of a failure can be detected, it is possible to avoid a sudden production decrease of the factory by replacing the spindle beforehand.
As a method and an apparatus for performing performance evaluation of a bearing, Japanese Patent Application Laid-Open No. 2009-80092 describes a bearing-friction measuring method and a bearing-friction measuring apparatus for supporting a rotating body on a measurement target bearing, rotating the rotating body, in a state in which the rotating body is rotating, interrupting transmission of rotation torque, causing the rotating body to self-rotate with inertia, calculating friction torque of the bearing on the basis of rotation angular velocity and an inertial moment of the rotating body at the time of the self-rotation, measuring friction of the bearing, and evaluating the performance of the bearing.
When it is attempted to measure a deteriorated state of the spindle, the bearing-friction measuring method and the bearing-friction measuring apparatus described in Japanese Patent Application Laid-Open No. 2009-80092 cannot be applied. A dedicated bearing-friction measuring apparatus is necessary for the bearing-friction measuring method described in Japanese Patent Application Laid-Open No. 2009-80092. The bearing-friction measuring method is not a method of inspecting a bearing attached to a machine tool. Therefore, it may be impossible to detect a deteriorated state of a spindle (a deteriorated state of a spindle bearing) in a usable state of a machine tool without disassembling a spindle head.